System and Method for Concentrating Sunlight

ABSTRACT

A system for concentrating solar energy is provided. The solar concentrating system uses a membrane formed of a flexible material to form either a reflective or refractive surface of a predefined shape. A quantity of fluid disposed on the membrane deforms the membrane into the predefined shape. In one embodiment the fluid is a liquid and the deformation of the membrane is determined by the mass of fluid and the effect of gravity. In another embodiment, the fluid is a gas and the deformation of the membrane is determined by the pressure of the gas contained in a cavity formed by the membrane on the bottom and a transparent layer forming the top surface of the cavity.

I. FIELD OF THE INVENTION

The present invention relates generally to the field of energyproduction; and more specifically to a system and method forconcentrating sunlight for electrical energy generation.

II. BACKGROUND OF THE DISCLOSURE

Concentrated solar power systems use mirrors and/or lenses toconcentrate sunlight so that it may be harnessed to generateelectricity. Dish-stirling systems generate electricity using areflective parabolic dish that tracks the sun to focus sunlight onto astirling engine. Other systems use fresnel lenses or concave mirrors toconcentrate sunlight onto a solar cell for electricity generation. Fewersolar cells are needed to utilize a given area of insulation because theoptics concentrate the sunlight from the given area onto a smaller areaof fewer solar cells. These systems have economic advantages overun-concentrated solar cell systems due to the relative high cost ofsolar cells compared to the lower cost of the concentrating optics.

An object of the present invention is to concentrate sunlight using anoptical system that is less expensive than conventional optics.

III. SUMMARY OF THE DISCLOSURE

An embodiment of the present invention is a system for concentratingsolar energy for the purpose of harnessing solar energy and/orconverting the solar energy into electrical or thermal energy. Opticalelements, such as lenses and reflectors, are used to concentratesunlight. These optical elements consist of a transparent fluid, whichacts as a refractive material, contained in a flexible sheet impermeableto the fluid, such as mylar. The fluid can be a liquid such as water.

The sheet is suspended between two parallel support structures so thatthe sheet's shape is formed by the force of gravity. The sheet forms thebottom wall of a fluid-holding container. The two vertically scalingwalls of the container may be an extension of the transparent sheetmaterial or another material impermeable to the contained fluid that isbonded to the sheet. The uppermost wall is a material such as mylarsheet or acrylic.

Because the liquid filled lens cannot move to track the sun and stillmaintain its shape, a system of mirrors tracks the sun during the day tocreate an image of the sun at zenith so that the sun's rays incident tothe lens are parallel to the lens's optical axis. One mirror tracks thesun to reflect the sunlight to another mirror positioned above thelenses which then reflects the sunlight downward.

An alternative embodiment of the present invention uses a gaseous fluid,such as air, disposed at a predefined pressure within a sealed opticalelement structure. The element structure has a top surface constructedof a transparent material that maybe either flexible or rigid, and abottom surface constructed of a flexible material. The bottom surfacecan be reflective, thus forming a reflective optical element.

Another embodiment of the present invention is a system forconcentrating solar energy. The system includes a membrane surfaceconstructed of a thin flexible material; a quantity of fluid having apredefined index of refraction. The quantity of fluid is disposed on atop surface of the membrane surface and deforms the membrane surfaceinto a surface having a predefined cross-section. Also a supportstructure is provided for supporting the membrane surface and thequantity of fluid. The support structure allows the membrane surface todeform under the influence of the quantity of fluid and gravity.

Another embodiment of the present invention is a system forconcentrating solar energy onto a heat pipe. The system includes anoptically transparent top layer; an optically reflective bottom layer,the bottom layer being a flexible material; and a frame bonded to thetop layer and the bottom layer forming an air-tight cavity therebetween.The cavity is filled with a gas at a predetermined pressure fordeforming the bottom layer into an arc cross-section.

IV. BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings wherein:

FIG. 1 illustrates a system for concentrating sunlight, in accordancewith the present invention;

FIG. 2 illustrates a perspective view of one embodiment that producesnine areas of concentrated solar energy, in accordance with the presentinvention;

FIG. 3 illustrates two orthogonal views of a single lens, in accordancewith the present invention; and

FIG. 4 illustrates two orthogonal views of a two-lens system, inaccordance with the present invention;

FIG. 5 illustrates a reflective embodiment of the present invention;

FIG. 6 illustrates another embodiment of the present invention; and

FIG. 7 illustrates orthogonal views of the embodiments shown in FIG. 5and FIG. 6.

V. DETAILED DESCRIPTION OF DISCLOSURE

Referring to FIGS. 1, 2, and 3 the solar energy concentration system 100consists of the transparent sheet 103, containing a fluid having anindex of refraction greater than air and constrained to the curvature ofthe transparent sheet 103. The transparent sheet 103 is suspendedbetween two parallel support structures 202. These parallel supportstructures 202, fluid, and lens side walls 303 comprise a lens thatconverges light in one dimension. The fluid is sealed between thetransparent sheet 103, lens side walls 303, and an upper transparentwall 302. Two lens frames 104 support the lenses so that they may besuspended above the ground in a manner allowing adjustment of the angleof the lens frame 104 with respect to the ground. Support pillars 101support the lens frame 104. A stationary mirror 106 is supported by amirror frame 203 and the mirror support structure 105. The stationarymirror 106 is angled such that the incident rays, being parallel to theearth's axis of rotation, are reflected downward producing an image ofthe sun at zenith 120. The sun's rays 108 incident to the stationarymirror 106 are reflected off of the tracking mirror 107, which tracksthe sun 121 throughout the day to provide stationary mirror 106 withincident rays that are parallel to the earth's axis of rotation.Tracking of the sun is accomplished by a motorized equatorial mount 109,which allows motion in right ascension R.A. and declination. Theconcentrated sunlight is directed towards the solar cells 110 where itis converted into electricity. Alternatively, the sunlight can bedirected to heat engines or any other suitable energy conversion deviceinstead of the solar cells 110.

FIG. 3 shows two orthogonal views of a single lens. The lens is shown tofocus light rays 307 one-dimensionally to a line of highestconcentration 310. This line of concentrated solar energy may be used inother embodiments of the invention not specifically illustrated if, forexample, the energy is to be focused onto a fluid containing pipe or alinear array of solar cells.

FIG. 4 shows the effect of adding a second lens with parallel supportstructures 405 running perpendicular to the first. This focuses sunlighttwo-dimensionally to create a spot of concentrated sunlight incident onsolar cells 110 instead of a line 310 as in FIG. 3.

Alternatively, in place of a refractive lens system, an embodiment shownin FIG. 5 uses a reflective surface 501. In the present embodiment, thereflective surface made of a thin, light flexible material is shapedinto a surface having a cross-section formed due to the weight of fluid503 held in the cavity 505 formed by the curvature of the reflectivesurface 501.

The reflective surface 501 is mounted on a rotating support assembly 507that allows the reflective surface 501 to rotate in synchrony with themotion of the sun throughout a full day. The rotating support assembly507 includes support legs 519 terminating in wheels 521. A set of guiderails 523 form a circular course over which the wheels 521 travel. Therotation of the reflective surface 501 is performed in order to maximizethe amount of sunlight impacting a thermally conductive pipe 509 (i.e.,heat pipe).

The thermally conductive pipe 509 is suspended above the reflectivesurface 501 running parallel to a horizontal axis. The pipe 509 ispositioned at or near a focal point in order to absorb energy fromsunlight incident to the pipe 509. The pipe 509 is disposed with wateror other fluid having a high thermal conductivity. The fluid circulatesthrough the pipe 509, entering at one end in a cooled state, and exitingfrom the top in the form of heated fluid or gas, which is transported toa steam turbine by a collector pipe 511. Other energy conversion systemsmay be used in place of a steam turbine. Such alternative energyconversion systems include stirling engines, thermal-electric devices,etc. The fluid returns from the steam turbine, or other energyconversion system, by a feeder pipe 513 once the fluid has cooled.

The pipe 509 is joined to the feeder pipe 513 and collector pipe 511with a rotating coupling assembly at each end. The rotating couplingassembly allows the pipe 509 to rotate along with the reflective surfaceassembly 515. Additionally, support members 515 provide support to thepipe 509 and attach the pipe 509 to the rotating support assembly 507.Vertical dashed line 517 indicates the center of rotation of therotating support assembly 507.

Referring to FIG. 6, an embodiment of the present invention is shown inwhich the fluid is a gas. The optical element 600 is constructed of aframe 602 supporting a top layer 604 of transparent, gas impermeablematerial and a bottom layer 606 of either a reflective or transparentgas impermeable material. The frame 602 forms the perimeter of theoptical element 600. A filler plug 608 is disposed on a side of theframe 602. The filler plug 608 allows the optical element 600 to befilled with a gas, such as air.

The top layer 604 and the bottom layer 606 are bonded to the frame 602forming an air-tight cavity. Additionally, support members 610 aredisposed at opposite sides of the frame 602. The support members 610 areused for rotating and supporting the optical element 600 when ininstalled into the energy producing system, such as the system shown inFIG. 7.

When a gas such as air is pumped into the optical element 600 throughthe filler plug 608, the top layer material 604 and the bottom layer 606material expand and stretch to take on a circular cross-sectional shape,or a portion of a circular cross-section, based on the pressure of thegas inside the optical element 600. Thus, by controlling the pressure,the curvature of the optical element can be controlled as well.

Alternatively, the top layer 604 can be made of a rigid material such asglass or acrylic plastic. In this alternative construction only thebottom layer 606 of the optical element 600 will expand and stretch whenpressurized gas is introduced into the optical element 600.

A benefit of using a gas-filled optical element as shown in FIG. 6 anddescribed above, is that the shape of such an optical element is notappreciably affected by gravity. Consequently, unlike a liquid-filledembodiment, the gas-filled optical element can be used with a dual-axistacking system in which one axis is the altitude and the other is theazimuth (i.e., alt-az tracking). A dual axis tracking system allows forthe light rays incident to the heat pipe to be perpendicular to thesurface of the heat pipe surface, which in turn allow for betterefficiency.

FIG. 7 illustrates orthogonal views of a reflective optical element,such as the embodiments shown in FIG. 5 or FIG. 6, using a single axistracking system 700 a and 700 b. Additionally, for comparison,orthogonal views of a reflective optical element, such as theembodiments shown in FIG. 6, using a dual axis tracking alt-az system700 c and 700 d is shown.

Referring to view 700 a, the incident light rays 702 pass through thetransparent top surface 706, and impact the reflective surface 708.Support members 710 is bonded to the edge of the reflective surface 708and the transparent surface 706, such that the cavity formedtherebetween is either air or water tight depending on the particularembodiment. As can be seen, in view 700 a the reflected light rays 704appear to intersect at a relatively small spot.

Turning to view 700 b, a view of the optical element of view 700 a isshown from a 90° offset. As is evident from view 700 b with only asingle tracking axis, the incident light rays 702 from the sun will attimes throughout the day impact the reflective surface 708 atnon-perpendicular angles relative to the optical axis. The resultantreflected light rays 704 will similarly shift by an equal angle from theperpendicular.

Consequently, using a single axis tracking system necessitates having aheat pipe (not shown) that extends beyond the length of the opticalelement so that the angled reflected light rays 704 will still impactthe heat pipe. In addition, at sever incident angles, such as timesapproaching sunrise and sunset, the reflected light rays 704 at theextremes of the optical element will be internally reflected as a resultof the critical angle of the transparent surface 706. Moreover,reflected light rays 704 at these extreme angles will not efficientlyimpart all the reflected energy to the heat pipe, as some portion of thereflected light rays 704 may be reflected rather than absorbed by theheat pipe.

However, when a dual axis tracking system is used as in the opticalelement shown in view 700 c and corresponding orthogonal view 700 d, theincident light rays 702 are made to impact the reflective surface 708 atan angle parallel to the optical axis. Consequently, while the incidentlight rays 702 and reflected light rays 704 appear identical, or nearlyso in views 700 a and 700 c, the reflected light rays 704, as seen fromthe perspective of view 700 d, impact the heat pipe at a perpendicularangle.

The result is a more efficient transfer of energy from the incidentlight rays 702 to the heat pipe. Little to no internal reflection occurswhen the incident light rays 702 and the reflected light rays 704 areparallel to the optical axis of the transparent surface 706 and thereflective surface 708. Moreover, because the reflected light rays 704arrive at the same point along the heat pipe throughout the entire day,the heat pipe can be dimensioned to have the same length as the opticalelement.

Alternatively, the heat pipe described in the embodiments above can bereplaced with photovoltaic elements (solar cells) or otherdirect-to-electricity conversion devices.

The direct embodiments of the present invention are intended to beillustrative rather than restrictive, and are not intended to representevery embodiment of the present invention. Various modifications andvariations can be made without departing from the spirit or scope of theinvention.

1. A system for concentrating solar energy, said system comprising: amembrane surface constructed of a thin flexible material; a quantity offluid having a predefined index of refraction, said quantity of fluidbeing disposed on a top surface of said membrane surface for deformingsaid membrane surface into a surface having a predefined cross-section;a support structure for supporting said membrane surface and saidquantity of fluid, said support structure allowing said membrane surfaceto deform under the influence of said quantity of fluid and gravity. 2.The system as in claim 1, further comprising: a solar collectingapparatus for collecting solar energy and converting said solar energyto a second form of energy.
 3. The system as in claim 2, wherein saidsolar collecting apparatus is formed of at least one photovoltaic celladapted for receiving concentrated solar energy.
 4. The system as inclaim 2, wherein said solar collecting apparatus is a heat pipe.
 5. Thesystem as in claim 1, further comprising: a rotating base supportingsaid support structure; and a tracking unit for controlling the azimuthof said rotating base to track a movement of a sun across a sky andorient said membrane surface to maximize incidence of said solar energyonto said membrane surface.
 6. The system as in claim 5, furthercomprising an altitude tracking system for adjusting said angle of saidmembrane surface to maximize incident solar energy.
 7. The system as inclaim 1, further comprising: at least one flat reflective surfacepositioned remotely of said membrane surface; and a tracking unit forcontrolling said position of said at least one flat reflective surfaceto track a movement of said sun across said sky and orient said flatreflective surface to maximize incidence of said solar energy onto saidmembrane surface.
 8. The system as in claim 1, wherein said membranesurface is reflective of at least a portion of wavelengths of said solarenergy.
 9. The system as in claim 1, wherein said membrane surface istransparent of at least a portion of wavelengths of said solar energy.10. The system as in claim 1, further comprising: a second membranesurface, transparent to at least a portion of wavelengths of said solarenergy, said second membrane surface being disposed above said membranesurface and deformed by a second quantity of fluid; and a second supportstructure for supporting said second membrane surface.
 11. The system asin claim 1, wherein said fluid is a liquid.
 12. The system as in claim1, further comprising a covering surface formed of transparent materialfor sealingly holding said quantity of fluid between said membranesurface and said covering surface.
 13. The system as in claim 12,wherein said fluid is a gas.
 14. A system for concentrating solar energyonto a heat pipe, comprising: an optically transparent top layer; anoptically reflective bottom layer, said bottom layer being a flexiblematerial; and a frame bonded to said top layer and said bottom layerforming an air-tight cavity therebetween, said cavity being filled witha gas at a predetermined pressure for deforming said bottom layer intoan substantial circular arc cross-section.
 15. The system as in claim14, further comprising a dual-axis tracking system for tracking theposition of a sun's motion throughout a day.
 16. The system as in claim14, wherein said top layer is a rigid material.
 17. The system as inclaim 14, wherein said top layer is a flexible material deformable bysaid gas filling said cavity.
 18. The system as in claim 14, furthercomprising a heat pipe of thermally conductive material and configuredfor transporting a thermal fluid across said system at a focal positionof light reflected by said bottom layer.